This invention relates a electromagnetic delay line and the manufacturing method thereof and particularly to a DIP lumped constant type delay line, to a variable distributed constant type delay line, and specifically to an SIP (Single-in-Package) distributed constant type delay line each having a small thickness.
A conventional lumped constant type delay line is formed by a plural number of inductance elements L1, L2, L3, L4 . . . and so on, each consisting of a ferrite bobbin having an I-shaped cross section around the body of which are wound enamel clad copper wires each of which is continuously disposed over the upper surface of an insulating substrate, and by a plural number of laminated ceramic condenser elements C1, C2, C3, C4, . . . and so on each of which is disposed continuously over the lower surface of the insulating substrate. A group of inductance elements and condenser elements will hereinafter be referred to simply as an inductor and a capacitor, respectively. The aforementioned inductor and capacitor are connected by conductive wires by connecting L1 and C1, L2 ad C2, L3 and C3 . . . and so on, respectively, thereby constituting a lumped constant type delay line circuit.
However, the conventional lumped constant type delay line is difficult to reduce in size especially in thickness because it is almost impossible to procure component parts for assembling which are smaller in shape. This structural limitation makes it harder to adopt an automation system in the production process thereof. Thus, much of the manufacturing process requires manual labor. Furthermore, the conventional distributed constant type delay line, especially one designed for a shorter delay time, has a drawback of creating an uncomputable inductance prevailing in the conductive wire connecting the inductor elements and capacitor elements, which prevents a high yielding of production and causes a higher manufacturing cost thereof.
An object of the present invention is to provide a lumped constant type delay line having a very small thickness but exhibiting superior performance that can be manufactured with lesser man-hours thereby overcoming the aforementioned problem.
A lumped constant type of delay line publicized in Japanese provisional publication (kokai-koho) showa 61 (1986)-45616 presents a structure wherein a connecting pin of an inductor bobbin is inserted into a through-hole defined in a substrate over the surface of which capacitor elements are disposed and the pin is immovably fastened to the substrate by applying solder paste or adhesive around the upper edge of the pin which is located within the through-hole to thereby connect the capacitor elements and the inductor elements.
However, Sn or Pb, a component of solder paste or other adhesive applied around the upper edge of the pin or over the capacitor elements tends to diffuse and cover the surface of the capacitor element or penetrate into the through-hole and cause an undesirable electrical connection.
Another object of this invention is to provide a lumped constant type delay line which provides an alternative to the use of solder paste or the like which can diffuse over the capacitor or into the through-hole whereby a normal electric connection between the capacitor and the pin terminal is obtained.
A conventional distributed constant type delay line of an SIP type has an insulating substrate on one surface of which is disposed a ground electrode layer, and on another surface of which an inductance conductive layer is disposed. Thus, the insulating substrate functions as a dielectric to form a delay line circuit. The insulating substrate has an alumina base (Al.sub.2 O.sub.3 90-99%) having dielectric constant of s=8-11. Furthermore, the ground electrode layer and inductance conductive layer are formed by a thin layer of neckle film or the like, respectively.
One end of the insulating substrate extends between bifurcated ends of a lead terminal, each end thereof being fitted by soldering paste to one end of the ground electrode layer and one end of the inductance conductor layer, respectively, to effect electrical connection therebetween.
The structure of the conventional distributed constant type SIP delay line also involves some problems. An alumina base substrate adopted as a dielectric usually has a fixed dielectric constant(s) which tends to put some limitation on designing various types of delay lines having a different delay time and characteristic impedance because of the thickness of the substrate is only the factor available to create fluctuations of capacitance as long as a balanced relation between a delay time and characteristic impedance exist within a limit based on the following equations:
L=Td.Zo PA2 C=Td/Zo
where:
Td: Delay time PA1 Zo: Characteristic Impedance PA1 L: Inductance PA1 C: Capacitance
Therefore, it may be impossible to design a variety of delay line circuits as desired.
And, forming thin film layers of inductors and capacitors requires man power and skill with a resultant rise in the production cost thereof.
Another object of this invention is to present means to overcome the aforementioned problems by adopting a composite which is a mixture of glass and dielectric material such as BaTiO.sub.3 as a dielectric layer which enables the selection of desired dielectic constant when designing various delay lines.